How to get larger version of author avatar

I am trying to incorporate author avatars into my posts by doing <?php echo get_avatar( get_the_author_meta('ID'), 150 ); ?> but I can’t go larger than 50x50px without it getting stretched (since the image is only 50x50px). It is using the BuddyPress thumbnail of the avatar.

How can I get it to use a larger thumbnail version or is there another function I can try?

I found the function that makes up bp_post_author_avatar() and then changed the type to full. Place this funtion in functions.php and use the new function to call the post author avatar in the template.

function fod_post_author_avatar() {
global $post;

if ( function_exists('bp_core_fetch_avatar') ) {
    echo apply_filters( 'bp_post_author_avatar', bp_core_fetch_avatar( array( 'item_id' => $post->post_author, 'type' => 'full' ) ) );  
} else if ( function_exists('get_avatar') ) {
    get_avatar();
}
}